Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased charge cooling due to its increased heat capacity compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. In this way, improved engine fuel economy may be achieved.
However, the inventors herein have recognized several issues with such an approach. Specifically, distribution of separate fuels for a vehicle may require significant infrastructure changes, and in some locations, both fuels may not be available.
Thus, in one approach, the above issues may be addressed by using water (or a water-alcohol blend, such as water/ethanol) injection to generate charge cooling. By using a fluid with at least some water, at least under some conditions, it is possible to enable operation under increased compression ratio and/or increased boosting while reducing knock issues even if the second fuel is not always available, or only limited amounts are available. However, as the amount of water in the fluid may vary, engine parameters may need to be adjusted based on the relative amount of water, such as a water fraction, for example.
As such, in one example, a system for an engine of a vehicle traveling on the road is provided. The system comprises a cylinder located in the engine; a delivery system configured to delivery fuel and a fluid to at least an engine cylinder of the while the vehicle is traveling on the road, said fluid containing at least some water; and a controller for varying an engine operating parameter based on an amount of water in said fluid, where said amount is determined based on an operating condition.
In this way, it is possible to accommodate and account for variation in an amount of water delivered to the engine, and thereby improve overall engine performance. Also, the system is applicable to situations other than vehicles traveling on the road.